Toxicologists Reveal Popular Weed Killer May Harm Teenage Brains

The widespread use of weed killer could be seriously damaging our teenagers’ brains, scientists warn.

As of 2021, 1.7 million metric tons of herbicides were used annually around the world, according to data from the UN’s Food and Agriculture Organisation, with 457,390 tons used in the U.S. alone. These chemicals can linger on our fruit and vegetables and seep into our waterways, meaning that many of us are ingesting them in small quantities on a regular basis.

“There is considerable use of herbicides and insecticides in agricultural industries in both developed and developing nations around the world, raising exposure potential for children and adults, especially if they live in agricultural areas, but we don’t know how it impacts each stage of life,” Briana Chronister, doctoral candidate at the UC San Diego, California, said in a statement.

Together with researchers from UC San Diego and Emory University, Chronister collected data from 519 adolescents aged between 11 and 17 in Pedro Moncayo, an agricultural county in Ecuador. By analyzing their urine, the team found that 98 percent of these individuals contained traces of glyphosate—known commercially as Roundup—the most widely used herbicide in the United States. Sixty-six percent of the participants’ urine also contained the broadleaf herbicide 2,4-D.

Following this analysis, the team assessed the participants’ cognitive performance in five key areas: attention and inhibitory control; memory and learning; language; visuospatial processing; and social perception.

From this assessment, the team found that individuals with higher levels of 2,4-D in their urine were more likely to perform poorly in their assessment for attention, memory and learning, and language. Meanwhile, those who had higher concentrations of glyphosate were more likely to perform poorly in social-perception tests. The results were published in the journal Environmental Health Perspectives on October 11.

The team also tested the effects of high levels of the insect-repellent DEET in the participants’ urine but did not find any significant associations.

Of course, this study was performed on a relatively small group of individuals in an agricultural community, which is not the environment that most American teenagers grow up in. These links may also be due to some other confounding factors, like spending more time on the farm than in formal education. However, these results are still striking and important to consider for young people in farming communities (and non-farming communities) around the world.

“Many chronic diseases and mental-health disorders in adolescents and young adults have increased over the last two decades worldwide, and exposure to neurotoxic contaminants in the environment could explain a part of this increase,” senior author Jose Ricardo Suarez, an associate professor in the Herbert Wertheim School of Public Health, said in a statement.

“Hundreds of new chemicals are released into the market each year, and more than 80,000 chemicals are registered for use today,” Suarez added. “Sadly, very little is known about the safety and long-term effects on humans for most of these chemicals. Additional research is needed to truly understand the impact.”